ABSTRACT Physical activity (PA) in children can promote a healthy body weight and reduce cardiometabolic risk factors.1-7 However, 58% of children aged 6-11 yrs do not meet the recommendation for 60 minutes of moderate-to- vigorous PA per day.8 Both neighborhood characteristics20-28 and parent behaviors23-37 influence child PA patterns. However, less is known about how these variables influence PA among low-income preschool children.24-28 Parents play a more central role in supporting the PA of preschool-aged compared with older children. Parent behaviors that support their child's PA are influenced by the resources and challenges in their neighborhood environment.23-28 Potential important parent moderators of neighborhood effects on child PA include parent perceptions of the neighborhood environment and parent behaviors that take advantage of neighborhood resources that support their child's PA. The field can be advanced by identifying how the low- income neighborhood environment and parent supportive behaviors interact to support preschool-aged child PA. Interventions that target modifiable parent supportive behaviors are critical. However, interventions can be effective only if key effective parent supportive behaviors are known. This requires prospective data collected from both parent and child. Temporal associations between neighborhood environment, parent supportive behaviors and preschool aged child PA have rarely been examined.23-28,30-37 The proposed research is a secondary data analysis to examine longitudinal associations between low-income neighborhood variables, parent supportive behaviors for child PA, and child PA. Data are from 534 low-income, ethnically/racially diverse parent-child dyads that participated in a three-year community-based obesity prevention intervention. Children were aged 2-4 years at baseline. Follow up retention rates were > 90% at 12, 24, and 36 months. The proposed study will address a set of distinct scientific questions that are outside the scope of the parent NET-Works study. The specific aims for the proposed research address the influence of low-income neighborhood environments and parent supportive behaviors on changes in child PA. The potential role of parent supportive behaviors as an intervention mediator of changes in child PA is examined.